Deoxidizing copper base metal parts



United States Patent DEOXIDIZING COPPER BASE METAL PARTS John Toth, Dearborn, Mich., assignor to Ford Motor Company, Dearborn, Mich., a corporation of Delaware No Drawing. Application June 1, 1954, Serial No. 433,813

2 Claims. (Cl. 134-3) This invention deals with metallurgy of the copper base alloys and more specifically with a method for deoxidizing the surfaces of such metals prior to soldering and in maintaining the surfaces so deoxidized.

This invention was developed to facilitate the manufacture of vehicular radiators, the working portions of which are copper and brass. However, this invention is not so limited but may be applied wherever the problem of deoxidizing the surface of copper base alloys exists. The manufacture of vehicular radiators is troublesome from a deoxidation standpoint, in that deep drawing operations are involved which necessitate a thermal stress relief operation which is normally carried out in an ordinary air atmosphere. At these elevated temperatures, an adherent oxide film is formed on the metal which must be removed prior to subsequent soldering operations. In the automotive industry this is conventionally done by immersing the parts in an acid solution containing about one third sulphuric acid, one third nitric acid, and one third water by volume. Occasionally, chromic acid is also added to this solution as a reoxidation inhibiter. An acid solution of this type readily dissolves the metal oxides as well as the base metal, and hence leaves a metal surface free of oxides. However, this solution is followed by a water rinse which inevitably becomes contaminated with acids carried over sufficient to render the wash solution oxidizing to the alloys. However, this acid is too weak to dissolve the oxides formed and hence the metal surface is again contaminated by oxides.

The art has had recourse to the use of both chromates and cyanides to inhibit respectively reoxidation during washing and reoxidation due to exposure to the atmosphere prior to soldering. However, both of these expedients leave an objectionable film on the surface of the metal.

To avoid these disadvantages of the prior art, I have developed a mixture comprising three essential ingredicuts:

1. A chemical compound selected from the group of thio-compounds, especially one containing a divalent sulphur atom, capable of replacing oxygen.

2. An oxyboron compound.

3. A chemical compound selected from'the group of anionic surface active agents known as sulphonates.

An example of such a formulation is:

Percent Sodium thiosulphate 65 to 85 Sodium tetra borate 12 to 24 An alkyl aryl sulphonate 5 to l b I 2,726,970 Patented Dec. 13, 1955 The above ingredients are mixed dry until a homogeneous mixture is obtained. Optimpm results have been obtained withliper cent sodium thio sulphate, 1 8 mgent sodium tetra borate and 7 per cent of an alkyl aryl sulphonate. To accomplish a homogeneous mixture, the dry compounds should have a reasonable screen analy- SIS.

This mixture is employed at a concentration between /2 and 16 ounces per gallon of water, The optjmum ran e is 4 to 8 ounces per gallon of water. This solution may be tspjegi ed at any temperature belgw 112.. F. but for most applications the ordinary room temperature solutions are quite effective. The time of immersion is not critical and can vary from V2 min'uTE' to 5 minutes.

Parts to be treated by this material are first cleansed in an alkaline solution, then rinsed in cold water, then deoxidized in the strong sulphuric, nitric acid solution described above, then quickly rinsed twice in cold running water. The surface is now clean and free from oxide contamination and is immersed in the solution described in this specification. This solution removes secondary oxides, neutralizes trace acids, destroys all traces of oxidizing materials and inhibits the surface of the metal against room temperature atmospheric reoxidation. The parts are now rinsed in hot water and permitted to air dry. Parts so treated may be stored any reasonable length of time without deleterious oxidation and when assembled for soldering the solder will penetrate perfectly between the faying surfaces indicating chemically clean metal.

I claim as my invention:

1. The process of preparing copper base metal parts for subsequent soldering operations comprising treating said parts first within an alkaline cleaning medium, then deoxidizing the surface by treating with a mixtureof sulphuric and nitric acids, and then treating the deoxidized surface with a solution of /2 to 16 ounces of a mixture comprising sodium thiosulphate, to 85 per cent, sodium tetraborate, 12 to 24 per cent and an alkyl aryl sulphonate, 5 to 10 per cent in one gallon of water.

2. The process of preparing copper base metal parts for subsequent soldering operations comprising treating said parts first with an alkaline cleaning medium, then deoxidizing the surface by treating with a mixture of sulphuric and nitric acids, and then treating the deoxidized surface with a solution of 4 to 8 ounces of a mixture consisting substantially of per cent sodium thiosulphate, 18 per cent sodium tetraborate and 7 per cent of an alkyl aryl sulphonate in one gallon of water.

References Cited in the file of this patent UNITED STATES PATENTS 1,049,054 Coombs --'Dec. 21, 1912 2,093,824 Woronoff Sept. 21, 1937 2,244,526 MacKay June 3, 1941 2,395,694 Spence Feb. 26, 1946 2,472,684 Rossi June 7, 1949 2,479,628 Kuentzel Aug. 23, 1949 FOREIGN PATENTS 878,043 France I an. 8, 1943 

1. THE PROCESS OF PREPARING COPPER BASE METAL PARTS FOR SUBSEQUENT SOLDERING OPERATIONS COMPRISING TREATING SAID PARTS FIRST WITHIN AN ALKALINE CLEANING MEDIUM, THEN DEOXIDIZING THE SURFACE BY TREATING WITH A MIXTURE OF SULPHURIC AND NITRIC ACID, AND THEN TREATING THE DEOXIDIZED SURFACE WITH A SOLUTION OF 1/2 TO 16 OUNCES OF A MIXTURE COMPRISING SODIUM THIOSULPHATE, 65 TO 85 PER CENT, SODIUM TETRABORATE, 12 TO 24 PER CENT AND AN ALKYL ARYL SULPHONATE, 5 TO 10 CENT IN ONE GALLON OF WATER. 